Pick the rosemary leaves into a pestle and mortar, add a pinch of sea salt and bash well. Finely grate in the lemon zest and squeeze in half the juice, then muddle in 2 tablespoons of olive oil.
Use a sharp knife to slice into the chicken breasts, then open each one out flat like a book. Flatten slightly with the heel of your hand.
Pour the rosemary marinade over the chicken and leave to marinate for a few minutes.
Meanwhile, make the dressing by mixing the mustard with the remaining lemon juice and twice as much extra virgin olive oil.
Place the tomatoes onto a tray, season and roast for 20 minutes.
Trim the beans, then cook in a pan of boiling salted water for 5 minutes. Drain and toss them in the mustard dressing, then add the roasted tomatoes.
Preheat a griddle pan or barbecue.
Grill the chicken breasts for 5 minutes, or until golden and cooked through, turning regularly, then serve with the warm beans and tomatoes.